headlines at the Oscar Pistorius trial. He's undergoing a brutal cross-examination. ABC's Matt Gutman is in Pretoria, South Africa. Good morning, Matt. Reporter: Good morning, Lara. That's right. It was a ruthless cross-examination this morning, unlike anything that we've ever seen here. The prosecution tearing into Pistorius, forcing him to view images so graphic, that people in the courtroom had to avert their gaze. Demanding again and again, that he take responsibility for killing his girlfriend. I made a mistake. You killed reeva steenkamp. That's what you did. Reporter: This morning, the lead prosecutor putting Pistorius on the ropes. What was your mistake? My mistake was that I took reeva's life. Reporter: This morning, Pistorius seemed more composed, after disintegrating into wailing sobs Tuesday. The judge even walking out. Reporter: Prosecutor knowns a the pit bull here, smelling blood. Attacking. Say, yes. I killed reeva steenkamp. I did. Reporter: Shooting his girlfriend on Valentine's day last year. Earlier, describing the horror of finding her there. And then I just sat there and waited for the ambulance to arrive. And -- I had my fingers in her mouth to help her try breathe. Reporter: But she would die in his arms. Reeva had already died whilst I was holding her. Before the ambulance arrived. So, I knew there was nothing that I could do for her. Reporter: And just minutes earlier, we heard Pistorius announce for the first time. I did not intent to kill reeva or anybody else. Reporter: Despite exploding four bullets into a tiny bathroom cubicle, at a person he said he thought was an intruder. Coming up, we'll show you the video and the questions that triggered a shouting match in court. A moment so raw, that it drew an outburst from Pistorius. Images so graphic, that the judge had to put an end to it.

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